1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display device, and more particularly to a method of manufacturing a liquid crystal display device having a reduced time for manufacturing the liquid crystal display device and an enhanced productivity.
2. Description of the Related Art
In general, a liquid crystal display device is lighter and smaller in comparison with other display devices. The liquid crystal display devices are manufactured via many manufacturing processes.
A first process for manufacturing the liquid crystal display device includes forming thin film transistor (TFT) unit cells on a first mother substrate and forming color filter unit cells on a second mother substrate. One example of the first process for manufacturing the liquid crystal display device is disclosed in U.S. Pat. No. 6,391,137 (entitled ‘method for manufacturing display device’).
A second process for manufacturing the liquid crystal display device includes a rubbing process. Liquid crystal layer disposed between the thin film transistor unit cell and the color filter unit cell is aligned via the rubbing process on the thin film transistor unit cells and the color filter unit cells. One example of the second process is disclosed in U.S. Pat. No. 5,879,497 (entitled ‘alignment device and rubbing cloth for alignment with respect to liquid crystal display device-use substrate, and method for manufacturing a liquid crystal display device’). A cylindrical roller covered by a piled fabric (or rubbing cloth) having pile rolls on the alignment film, so that an alignment groove is formed on the alignment film. The alignment groove creates pre-tilt angles of liquid crystal molecules of the liquid crystal layer.
One example of a third process for manufacturing the liquid crystal display device is disclosed in the U.S. Pat. No. 6,397,137. The third process includes an assembly process for assembling the first mother substrate and the second mother substrate. The first mother substrate and second mother substrate are assembled such that the thin film transistor unit cells of the first mother substrate face the color filter unit cells of the second mother substrate unit cell. Hereinafter, the first mother substrate and second mother substrate are referred to as an ‘assembled substrate’, and the thin film transistor unit cell and color filter unit cell are referred to as a ‘liquid crystal display device unit cell’.
One example of a fourth process for manufacturing the liquid crystal display device is disclosed in the U.S. Pat. No. 6,397,137. The fourth process includes a scribe-and-break process for scribing and separating the liquid crystal display device unit cells from the assembled substrate. One liquid crystal display device unit cell separated from the assembled substrate is referred to as a ‘liquid crystal display panel’.
A fifth process for manufacturing the liquid crystal display device includes a test process. A test driving signal is applied to the liquid crystal display panel for testing the liquid crystal display panel.
A sixth process for manufacturing the liquid crystal display device includes a liquid crystal injection process for injecting liquid crystal into a cell gap disposed between the first mother substrate and the second mother substrate, and cell gap modulating process for modulating the size of the cell gap.
A seventh process for manufacturing the liquid crystal display device includes a polarizing plate attaching process and module process. A polarizing plate (or polarizing plates) is (are) attached on the liquid crystal display panel via the polarizing plate attaching process. A driving module for driving the liquid crystal display panel is installed on the liquid crystal display panel via the module process. Hereinafter, the liquid crystal display device having the driving module is referred to as a ‘liquid crystal display panel assembly’.
Generally, the sequence of the conventional manufacturing processes has been maintained, and the failures occurring during each of the processes has been reduced.
However, the conventional manufacturing processes has some critical problems.
For example, a process speed of each of processes is different from each other. In detail, a process speed of the first through the third processes is different from that of the fourth through the seventh processes. In general, the process speed of the first through the third processes is faster than that of the fourth through the seventh processes. Namely, the process speed of the processes of manufacturing the thin film transistor unit cell, the color filter unit cell and the assembled substrate is faster than the process speed of the scribe process, separation process, the test process, the liquid crystal injection process, polarizing plate attaching process and the module process.
Therefore, the assembled substrate that has passed through the third process should stand by for a predetermined time so as to undergo the fourth process. The longer the assembled substrate stands by, the lower is the productivity of the liquid crystal display device.
More equipment may be established in the fourth through the seventh processes in order to solve above problem. In other word, extensions of equipment may increase the productivity of the liquid crystal display devices. However, the more equipment greatly increases manufacturing cost.
Further, the conventional manufacturing processes have many problems.
A first problem occurs in the rubbing process. The rubbing process for aligning the liquid crystal molecules has the following problem. The roller covered by a piled fabric having pile rolls on the alignment film, so that an alignment groove is formed on the alignment film. The alignment groove creates pre-tilt angles of liquid crystal molecules of the liquid crystal layer.
However, many particles are generated as a byproduct in the conventional rubbing process. The particles may induce failures during the rubbing process. In order to eliminate the particles, a cleaning process is needed. The cleaning process includes a chemical cleaning process in which chemical cleaning agent resolves the particles and the particles are removed, a process for removing the chemical cleaning agent by pure water, and a dry process for removing the pure water. Accordingly, the time for manufacturing the liquid crystal display device may be increased due to the cleaning process.
Further, according to the conventional rubbing process, the rubbing cloth is replaced by a new rubbing cloth or the rubbing cloth is cleaned periodically. Therefore, the conventional rubbing process cannot be successively performed and the efficiency of manufacturing the liquid crystal display device is lowered.
Moreover, in the conventional rubbing process, the piled fabric (rubbing cloth) having pile forms alignment grooves on the alignment film. Therefore, defects of the alignment grooves are seldom detected, when the alignment grooves are already formed. The defects of the alignment grooves may be detected in the reliability test of the liquid crystal display device after the liquid crystal display device is completely manufactured. The liquid crystal display device having a defect of the alignment groove lowers image display quality.
A second problem occurs after the assembled substrate is manufactured. When the assembled substrate is manufactured, the liquid crystal display device unit cells are separated from the assembled substrate, and each of the liquid crystal display panels are manufactured using each of the liquid crystal display device unit cells. Input terminals and (or) output terminals are exposed to the air, and the input/output terminals are oxidized, so that a thin oxidation film may be formed on the surface of the input/output terminals. The thin oxidation film deteriorates electrical characteristics of the input/output terminals. Therefore, display quality of the liquid crystal display device is lowered.
A fourth problem occurs in the module process. Liquid crystal is injected into liquid crystal display panel and a polarizing plate is attached onto the liquid crystal display panel. The polarizing plate is attached onto each of the liquid crystal display panels separated from the assembled substrate one by one. Therefore, much time is required so as to attach the polarizing plate onto the assembled substrate.
In order to overcome above problem, the polarizing plate may be attached onto the assembled substrate. Then, the polarizing plate attached onto the assembled substrate is cut off, so that a liquid crystal display device unit cell having a polarizing plate on is manufactured. However, it is hard to detect the defect of the liquid crystal display device unit cell before cutting off the assembled substrate. When a polarizing plate is attached onto a defective liquid crystal display unit cell, the polarizing plate is wasted.